Groeth on VRB-G

lamb L.A.M.Buisman at
Sat Apr 8 14:43:16 EST 2000

Tim Marsh wrote:

Were the control plates overlayed with agar at the same time as the plates in
the test? If not, maybe contamination took place while pouring the second
It could be that what grew is a strictly aerobic bacterium. Bacillus sp.? What
kind of sample was cultured?
Is it grampositive? Spores?
The next step depends on the kind of lab you're in, what tests are available.


> Dear All,
> A colleague has been carrying out tests for Enterobacteriaceae using VRB-G
> (Violet Red Bile agar with Glucose, produced by Oxoid) agar.  The test is
> carried out as a pour plate using VRB-G, which is also overlaid with VRB-G.
> Approx. 60 of the plates have grown creamy white colonies on the surface of
> the overlay (not in the original test sample layer).  I thought this might
> have been environmental contamination, but all control plates used show no
> growth.
> The limited microscopy so far performed indicates that they are bacterial:
> small rods (slightly longer than Listeria sp.) and are also motile.
> Can anyone enlighten me?  Can you suggest what they might be or what the
> next stage of diagnosis might be?
> Thank you for any help!
> Tim
> ( Please reply to tmarsh at )

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